The present invention relates in general to semiconductor device fabrication and, more particularly, to a vacuum chuck with a venturi jet for converting a positive pressure into a vacuum that securely holds a semiconductor wafer during manufacturing processes.
A common process in semiconductor device fabrication is chemical etching where material is removed from specific areas of the semiconductor wafer by a chemical process. Areas on one surface the semiconductor wafer not intended to be etched are first masked. A liquid etchant, for example hydrochloric acid, is applied to the reactive surface of the semiconductor wafer. The etchant chemically removes material from the unmasked areas. The wafer is typically spun at a high rate to evenly distribute the etchant during the process. Etching is also used for bulk removal of material in thinning processes to achieve specific electrical characteristics.
The semiconductor wafers are commonly processed one at a time to maintain strict processing standards. One technique involves holding the semiconductor wafer in place by grasping the edges of the wafer with pins during the etching process. It is undesirable to allow the etchant to reach the bottom unreactive surface of the semiconductor wafer. A nitrogen gas is blown onto the bottom of the semiconductor wafer to remove any etchant. As the etching process proceeds, the diameter of the semiconductor wafer reduces as material at the edge etches away. The grasping of the semiconductor wafer by the edge pins becomes less secure allowing movement of the wafer and possible damage.
To solve the pin grasping problems, vacuum chucks have been used to securely hold the semiconductor wafer in place. The semiconductor wafer is positioned on the vacuum chuck and a negative pressure (vacuum) is drawn through the vacuum chuck to create a suction that secures the wafer in place. Unfortunately, the negative pressure also tends to draw liquid etchant around the edge to the bottom side of the semiconductor wafer. The liquid etchant removes semiconductor material on the bottom side of the wafer which is undesirable. Attempts have been made to block the migration of etchant from the upper surface to the bottom side of the semiconductor wafer including polymer coating and taping, but most if not all techniques involve additional processing steps and complexity that add to the overall cost of manufacture.
Hence, a need exists for an apparatus that holds the wafer securely throughout the etching process and further prevent the etchant from reaching the bottom side of the semiconductor wafer.